This invention relates to a tapered roller bearing and more particularly to a tapered roller bearing device which supports a pinion shaft, for example, of a final reduction gear (differential gear) of an automobile, and is lubricated by lubricating oil received within the bearing device.
In a conventional tapered roller bearing as shown in FIG. 23, a plurality of tapered rollers 230 are rollably disposed between a raceway surface 211 of an inner ring 210 and a raceway surface 221 of an outer ring 220 in such a manner that a large end surface 232 of each tapered roller 230 is slidingly guided by a roller guide surface 213 of a rib 212 of the inner ring 210 while a small end surface 233 of each tapered roller 230 is slidingly guided by a roller guide surface 216 of a small rib 215 of the inner ring 210. A cage 240 having pockets 243 respectively holding the tapered rollers 230 is disposed between the two raceway surfaces 211 and 221.
There is also known a conventional tapered roller bearing (disclosed, for example, in JP-A-01-193411) so constructed as to prevent foreign matters from intruding into the interior of the bearing.
In this conventional tapered roller bearing, a first seal having a lip held in sliding contact with an inner peripheral surface of an outer ring is fixed to a small end portion of an inner ring. Further, a second seal having a lip held in sliding contact with an end surface of the outer ring is fixed to a large end portion of the inner ring. Lubricating oil flowed into the tapered roller bearing through the lip of the first seal forces the lip of the second seal open, and is discharged from the tapered roller bearing.
In the tapered roller bearing as shown in FIG. 23, a flow of a fluid from the small end side of the inner ring 210 toward the large end side thereof (that is, a pumping action due to a centrifugal force) develops during the rotation of the bearing.
Utilizing this pumping action, lubricating oil is supplied into the bearing from the small rib (215) side of the inner ring 210, and is discharged from the rib (212) side of the inner ring 210.
However, during the high-speed rotation of the bearing, the centrifugal force becomes high, so that the lubricating oil supplied to the small rib (215) side of the inner ring 210 tends to flow as indicated by arrow P′, and is liable to escape toward the outer ring 220. It is thought from this that the amount of supply of the lubricating oil to an area of contact between the large end surface 232 of each tapered roller 230 and the roller guide surface 213 of the rib 212 of the inner ring 210 becomes insufficient.
Particularly when the amount of supply of the lubricating oil is reduced in order to achieve a low-torque design of the tapered roller bearing so as to reduce a torque loss of a machinery, the amount of the lubricating oil supplied to the area of contact between the large end surface 232 of each tapered roller 230 and the roller guide surface 213 of the rib 212 of the inner ring 210 is liable to become insufficient, and this leads to a fear that seizure may occur.
Furthermore, in the tapered roller bearing disclosed in JP-A-01-193411, the lubricating oil resides within the bearing when the lip of the second seal is held in a closed condition, and an oil agitation loss is increased by this residing lubricating oil, so that a torque loss develops, and therefore the low-torque design can not be achieved.
Incidentally, the tapered roller bearing (see JP-A-2004-76766) which includes a plurality of tapered rollers disposed between an outer ring and an inner ring, and a cage holding these tapered rollers is compact, and can support large radial and axial loads, and besides can be used in a high-speed rotating operation. Therefore, such tapered roller bearings have been extensively used in a pinion shaft support apparatus for a vehicle, etc., as shown in JP-A-2000-170775.
FIG. 22 shows one example of a differential gear of the type in which a tapered roller bearing device of the present invention can be used. The differential gear includes a pinion shaft 442 rotatably supported on a housing 441 and having a pinion gear 443 provided at a rear end thereof, a ring gear 444 meshing with the pinion gear 443, a pair of inner and outer tapered roller bearings 445 and 446 rotatably supporting the pinion shaft 442 on the housing 441, and a drive shaft-connecting flange coupling 447 formed at an outer end of the pinion shaft 442.
In this differential gear, lubricating oil splashed up in accordance with the rotation of the ring gear 444 flows through a lubricating oil passageway 448 within the housing 441, and is introduced into a region between the pair of tapered roller bearing devices 445 and 446. When the tapered roller bearings 445 and 446 rotate, a flow of the fluid (a pumping action) from a small rib side of an inner ring of each bearing toward a rib side thereof occurs. Therefore, in the tapered roller bearings 445 and 446 used in the differential gear, the lubricating oil is supplied from the small rib side of the inner ring and is discharged from the rib side of the inner ring, utilizing this pumping action. This lubricating method is commonly used.
With the above conventional lubricating method, the lubricating oil can be easily introduced into each tapered roller bearing. However, during high-speed rotation, most of the lubricating oil flows toward an outer ring under the influence of a centrifugal force, and therefore the lubricating oil is not sufficiently distributed to the vicinity of the rib of the inner ring, and much heat is generated at an area of sliding contact between the rib of the inner ring and a large end surface of each tapered roller, and besides the generated heat can not be easily removed (that is, a temperature rise is liable to occur at localized areas), so that seizure is liable to develop.
On the other hand, in a pinion shaft support apparatus of a vehicle, etc., to reduce a running torque of a tapered roller bearing in order to achieve a low-loss design has been a global problem. For reducing the running torque, it is effective to reduce the amount of lubricating oil passing through the bearing to thereby suppress an oil agitation loss caused by the lubricating oil. However, when the amount of the lubricating oil is reduced, the risk of seizure of the rib increases, and therefore at present, a large amount of lubricating oil is supplied to the tapered roller bearing.